In 2008 Obama deployed the biggest grassroots party machine, armed with high-tech knowhow, in US political history. His re-election team continued to grow for this campaign, and he retains a commanding logistical lead in battlefield states. This firepower may prove crucial in a tight race.
According to Jim Messina, the President's campaign manager, the machine has two tasks - "One, to persuade the undecideds, and two, to turn our voters out".
Obama's job, greased by attack ads, is to work on the undecideds. And the field offices - about 800 across the US, mostly in swing states, compared to Romney's 300 - must motivate Democrats to go to the polls.
This discrepancy is most obvious in the swing states of Ohio, Florida and Virginia. Obama has 131 offices in Ohio to Romney's 40, 106 in Florida, compared to 47 and 61 in Virginia, compared to 30.
According to a random sample conducted by Atlantic magazine, the Obama offices - supplemented by community "staging locations" in the homes of volunteers - were primarily geared towards the President's re-election, while the Romney offices were focused on local candidates.
If Democrats excel at reaching voters by phone or at the door, this traditional approach is integrated with a digital strategy, in which Romney matches Obama. Spending on internet ads is expected to rise sixfold from 2008 to US$160 million.
Both campaigns have exploited YouTube, Twitter, Facebook, Flickr, Google, Tumblr and other platforms.
Team Obama enlisted celebrity endorsements, such as a YouTube video (5,170,305 hits by yesterday afternoon) posted by Buffy the Vampire Slayer director Joss Whedon.
His spoof warns of an impending "nightmare zombie apocalypse" of Romney cutbacks that "guarantee poverty, unemployment, overpopulation, disease and rioting ... he's not afraid to face a ravaging, grasping horde of subhumans. Because that's how he sees poor people already."
But the decisive innovation may be "micro-targeting", in which campaigns have collected more voter information than in any other race, so as to tailor their pitches to voters via on-line ads, phone calls and home visits.
For the first time data from publicly available voter files, social media, web surfing, canvassing and other sources has been amalgamated into databases that allow campaigns to target specific voters with unprecedented accuracy.
If attack ads are blunt instruments used to bludgeon TV viewers, micro-targeting allows campaigns to reach individuals.
"Micro-targeting is huge in the news this election cycle," says Brandi Travis, chief marketing officer with Aristotle, a bipartisan group used by Democrats and Republicans to obtain voter data since 1983.
"But it's something people have been doing for years. They're just doing it in more sophisticated ways."
Information is gleaned from public sources such as the US Census Bureau and the Federal Election Commission, and commercial marketing material which tracks charitable donations, surveys, social media, credit card purchases, magazine subscriptions and online behaviour.
Aristotle offers customers - including political campaigns, pollsters and consultants - 500 "data points", such as name, sex, age, race, address, email and phone contacts, voting history, party affiliation and personal interests. The key is to be precise.
"We know, say, if a person is a Republican, if they're interested in the environment, or if they've given to specific causes," explains Travis. "The biggest thing is not the micro-targeting, but how that data is used."
Exactly how campaigns use such data is a secret. But software crunches data to create algorithms and place voters into groups that are bombarded with tailored messages. A similar method was used by pollster John Zogby, who devised voter "neo-tribes".
Campaigns also buy access to "cookies", a digital footprint, to target voters with ads on websites visited.
Sometimes the message is delivered in person by a party canvasser. Aristotle supplies an application called Voter IQ. The Democrats have Dashboard, which gives canvassers "walk lists" of where to go and who to talk to.
Canvassers know which way voters lean or if they are undecided. Committed opponents are ignored. They know which issues interest specific voters. They also key in new information, say a voter's current cellphone number and email address, for future use, a prospect that alarms privacy advocates.
Some limits apply. Anyone, including political campaigns, who makes unsolicited robocalls - often autodialed - to cellphones, pagers or other mobile devices that are on a "do not call" list faces fines of up to $16,000 a call. Aristotle removes such numbers from its data.
Deciding if someone's personal comfort zone has been violated is a grey area. But data mining, algorithms and micro-targeting will keep pushing privacy boundaries.
Meanwhile, Aristotle and others are gathering data for the 2014 US midterm elections.
